Conventional hydraulic motors or jacks include a piston located in a hydraulic cylinder with a ram extended from the cylinder, and a manually operable control valve to admit hydraulic fluid under pressure to the pressure end of the cylinder during the working stroke of the piston. The manual control valve also operates to admit hydraulic fluid to the opposite end of the cylinder during the return stroke of the piston while providing for release of hydraulic fluid from the pressure end of the hydraulic cylinder. A lock-out device or valve is commonly interposed between the hydraulic motor and the control valve to isolate the motor from the control valve and the remainder of the system when the hydraulic motor is at rest and under load. This is done to prevent leakage and to remove stress from the control system which could otherwise result in system failure. Such devices usually include two separate check valves, one associated with the high pressure end of the hydraulic cylinder and the other associated with the lower pressure end of the cylinder. When fluid is introduced into one end of the cylinder, the fluid pressure is operative to open the valve asociated with that end of the cylinder, but it is necessary to provide means to open the other valve to permit release of fluid from the other end of the cylinder. This usually takes the form of a mechanism that assures that when one valve opens, the other also opens in proportionate degree. See, for example, U.S. Pat. No. 2,588,520 to Halgren. Commonly, this mechanism includes an actuator plunger which is moved by hydraulic fluid under pressure passing through one valve to a position where it mechanically opens or unseats the other valve to permit displaced fluid to pass through the other valve as fluid under pressure enters the first valve. This interrelationship of the check valves gives rise to pulsations or interruptions in the movement of the ram of the hydraulic cylinder. For example, upon the return stroke of the piston when a load is carried by the ram, hydraulic fluid is admitted to the low pressure side of the hydraulic cylinder while it is released from the high pressure side. Hydraulic fluid under pressure is effective to unseat the check valve associated with the low pressure side of the cylinder to permit entry of fluid. The actuating plunger is mechanically moved to a position where it unseats the check valve associated with the high pressure side of the cylinder to permit displacement of fluid from that side of the cylinder. As the hydraulic piston moves in the cylinder the pressure drops on the low pressure side of the cylinder causing the check valve associated with that side of the cylinder to move toward a closed position. This mechanically causes the check valve associated with the other end of the cylinder to move toward a closed position also. This causes an interruption of movement of the piston and ram temporarily until hydraulic fluid pressure builds up sufficiently to cause the check valve associated with the low pressure side of the cylinder to move towards the more open position which again moves the other check valve toward a more open position. The resulting pressure differential on the actuating plunger of the device accounts for pulsations or interruptions experienced during movement of the hydraulic ram and piston. The resulting chattering can cause structural damage.